CSC151.01 2015F, Class 26: Preconditions, Revisited =================================================== * New partners! * Don't forget to introduce yourselves! _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Lab. Preliminaries ------------- ### Admin * Review sessions this week * Monday 8pm (Zachary) * Wednesday 8pm (Zachary) * Thursday 8pm (Erin) * No Sam Thursday review :-( * I will be AFK (Away from Keyboard) starting about noon on Tuesday. If you have exam questions, ask them before then. * I sent out notes on the prologues from exam 2. If you don't regularly read your email, you should check for those notes. * Please don't ask tutors/mentors to answer questions on your exam code or to explain exam questions to you. ### Upcoming Work * Reading for Tuesday: [Characters and Strings](../readings/strings-reading.html) * [Exam 2](../assignments/exam.02.html) * Exam due in electronic form Tuesday night * Exam due in hardcopy Wednesday class time * Epilogue due Wednesday night * Today's Lab writeup (due before class Wednesday) * Email to * Subject: _CSC 151 Lab Writeup Class 26 (Your Names)_ * Exercises: 1f, 3h ### Extra Credit Opportunities * If possible, send me these in advance. #### Academic * Any visit to the current show in the Faulconer gallery * CS Table Tuesday, noon, White Dining Room, THERAC 25 (C) #### Peer Support * Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance. * Pun Club, Saturdays, 4pm, Way over Younker. * Study Abroad Session, Monday the 12th 7-8pm in JRC 101. Hear about Study Abroad Experiences and think about Study Abroad. ### Quiz 6 We'll look at the first problem. I'll probably return it tomorrow. ### An "Interesting" Use of Recursion You wrote something like: (define sample-and-replace-d! (lambda (image left top width height) (let ([color1 (random-sample image left top width height)] [color2 (random-sample image left top width height)] [color3 (random-sample image left top width height)]) (when (and (< (irgb-distance color1 color2) 50) (< (irgb-distance color2 color3) 50) (< (irgb-distance color3 color1) 50)) (fill-rectangle! image left top width height (irgb-average-3 color1 color2 color3)))))) We can use recursion! (cond [(and (< (irgb-distance color1 color2) 50) (< (irgb-distance color2 color3) 50) (< (irgb-distance color3 color1) 50)) (fill-rectangle! image left top width height (irgb-average-3 color1 color2 color3))] [else ; recurse on the top-left quarter ; recurse on the top-right quarter ; recurse on the bottom-left quarter ; recurson on the bottom-right quarter]) * Our base case is probably when width and height are small enough. ### Questions Problem 6: Two approaches * Approach 1: Clever use of `quotient` and `modulo`. * Approach 2: Given a row number and the number of columns, compute all the points in that row. Use `map` to generalize. _Question too complex to rephrase on the eboard._ > (map list (list "sam" "tyler" "bailey") (list "jones" "bailey" "doodle")) '(("sam" "jones") ("tyler" "bailey") ("bailey" "doodle")) > (map list (list 1 2 3) (list 4 5 6)) '((1 4) (2 5) (3 6)) _How many test cases on problem 1?_ > I came up with something like 3 x 2 x 3 x 4 approaches. I combined some things into a test of multiple concepts. I ended up with ten or so. _Are drawings that are not renderable (e.g. because they don't have any points that fall within a typical image) still drawings?_ > Yes. _Should we put an example in problem 1?_ > Yes. Show the first few lines of it failing massively on the incorrect implementation. _Should we get rid of the ugly X's?_ > That would be nice. You can keep beautiful X's, though. We do judge an X by it's appearance. (No, that joke failed miserably.) _What does `drawing-render!` do?_ > Puts a drawing on top of an existing image. > You should not need it for this exam. _Should we show experiments for everything?_ > Yes, that's why there's a section for experiments in every problem. Lab --- Writeup: 1f, 3h